During wild-type hermaphrodite development, 131 somatic cells undergo programmed cell death. Many genes involved in the execution of cell death have been identified, but the mechanisms controlling the decision by specific cells to undergo programmed cell death are still poorly understood: only six genes that control the programmed deaths of ten cells have been described. The four CEM neurons are especially convenient for studies of the regulation of programmed cell death, because the CEMs die during hermaphrodite development but survive and differentiate in males, and the
pkd-2::gfp cell-fate reporter (kindly provided by Maureen Barr and Paul Sternberg) can be used to rapidly score animals for the presence of CEMs. A genetic screen of 60,000 mutagenized haploid genomes recovered at least 154 independent mutations causing inappropriate survival of the CEMs in hermaphrodites. Three of these mutations,
n3713 ,
n3714 , and
n3720 , were gain-of-function mutations in the gene
ceh-30 ( ceh , C. elegans homeobox), which is required for CEM survival in males. These three alleles disrupt an evolutionarily conserved binding site for the transcriptional repressor TRA-1, which is required in hermaphrodites to prevent masculinization, and these mutations appear to cause the inappropriate expression of
ceh-30 in hermaphrodites and the consequent survival of the CEMs (see abstract by Schwartz and Horvitz). We performed several clonal screens, totaling nearly 7,000 mutagenized haploid genomes, for suppressors of
ceh-30(
n3714 gf ) . From these screens, we recovered at least 92 independent mutations causing the absence of GFP-positive CEMs in
pkd-2::gfp ;
ceh-30(
n3714 gf ) hermaphrodites. These suppressors include at least one loss-of-function mutation in
ceh-30 ,
n4111 , and at least one mutation,
n4132 , that prevents expression of the
pkd-2::gfp reporter (see 2003 International Worm Meeting abstract 461B by Wang and Barr). We are currently testing whether the disappearance of GFP-positive CEMs caused by our suppressors is affected by loss of function of
ced-3 or
ced-4 ( ced , cell death abnormality), genes required for all programmed cell deaths, and observing the effects of our suppressor mutations upon male CEM development. We hope to identify mutations that cause the CEMs to die by programmed cell death despite the protection of the
ceh-30(
n3714 gf ) mutation and mutations in genes required specifically for the regulation of
ceh-30 or that function downstream of or in parallel to
ceh-30 to regulate the male-specific survival of the CEMs. We also expect to identify mutations in genes required to properly determine the fate of the CEM neurons.